1. Field of the Invention
The present invention relates to a process for the preparation of orthocarbonates by reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol followed by oxidation of the resultant alkali metal cyanide or alkaline earth metal cyanide, extraction of the orthocarbonate, and distillative work-up of the extract.
2. Description of the Background
Orthocarbonates are valuable and versatile intermediates for the synthesis of a wide variety of classes of compound.
For example, OH-acidic compounds such as phenols or carboxylic acids can be etherified or esterified respectively using hydrocarbyl orthocarbonate esters. Furthermore, hydrocarbyl orthocarbonates exhibit characteristic, synthetically valuable reactions with amines, enol ethers, sulfonamides, and the like. (See, in this respect Synthesis 1977, pages 73-90).
Syntheses of orthocarbonates are known as disclosed in the literature. In most processes (see Synthesis 1977, pages 73-90), xcex1-branched radicals, such as, for example, the isopropyl radical, cannot be introduced into the orthocarbonate molecule.
DE-A 22 49 460 indicates a general process specification which can also be used for branched radicals. However, the document discloses that is particularly disadvantageous that the alkali metal chloride or alkaline earth metal chloride and alkali metal cyanide or alkaline earth metal cyanide formed in the reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alkanol be removed by filtration. Because of the very high toxicity of the cyanide salts, the implementation of high safety measures is necessary. The alkali metal cyanide or alkaline earth metal cyanide formed must subsequently be destroyed or disposed of separately. A need therefore continues to exist for an improved method of synthesizing orthocarbonates.
Accordingly, one object of the invention is to provide a process for the preparation of orthocarbonates which is technically simple and does not require a filtration step for removal of the salts formed in the reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol, wherein the alkali metal cyanide or alkaline earth metal cyanide formed is destroyed while still in the reaction batch.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a process for the preparation of orthocarbonates, by reacting trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol of the formula:
Rxe2x80x94OHxe2x80x83xe2x80x83(II) 
wherein R is an unsubstituted or substituted, saturated aliphatic or cycloaliphatic hydrocarbon radical in which the carbon atom of group R, linked to the oxygen atom of the alcohol, has at least one hydrogen atom, in a polar solvent, reacting the product obtained in water with an oxidant, extracting the organic-aqueous phase of the material obtained after oxidation; and
distilling the extracted material obtained and obtaining orthocarbonate product of the formula:
C(OR)4xe2x80x83xe2x80x83(I) 
wherein each R group is as defined above.
The objective of the invention is achieved by adding water after the reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol, extracting the product, and then working-up the product by distillation. Surprisingly, it has been found, in particular, that addition of a mixture of water and oxidant converts the alkali metal cyanide or alkaline earth metal cyanide formed in the reaction in the reaction batch to a nontoxic compound without the conversion resulting in a loss in the yield of orthocarbonate. Thus, the risk potential caused by the presence of an alkali metal cyanide or alkaline earth metal cyanide is reduced to a minimum.
The invention therefore relates to a process for the preparation of orthocarbonates of the general formula
C(OR)4xe2x80x83xe2x80x83(I) 
where R is an unsubstituted or substituted, saturated hydrocarbon radical in which the carbon atom linked to the oxygen atom has at least one hydrogen atom, by reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol of the general formula
Rxe2x80x94OHxe2x80x83xe2x80x83(II) 
where R is as defined above, oxidation of the resultant alkali metal cyanide or alkaline earth metal cyanide, extraction of the orthocarbonate, and distillative work-up of the extract.
In formulas (I) and (II) the substituted or unsubstituted, saturated radical R can be a linear or branched alkyl radical, in particular one having 1 to 7, preferably 1 to 4, carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl or neopentyl, or a cycloalkyl radical, in particular having 3 to 8 carbon atoms, such as, for example, cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl, or a cycloalkylalkyl radical, such as, for example, cyclopropylmethyl, cyclopentyl methyl or cyclohexylmethyl. In other words, the carbon atom of the aliphatic group R linked to the oxygen atom of the alcohol compound does not have a hydrogen atom attached thereto. That is, tertiary groups are excluded as aliphatic groups of the alcohol.
In the radicals denoted by R, one or more hydrogen atoms may be replaced by substituents, such as, for example, alkoxy groups, aryloxy groups or dialkyl and/or -aryl-substituted amino groups.
The process for the preparation of orthocarbonates of the present invention comprises the following reaction and process steps:
reaction of trichloroacetonitrile with an alkali metal salt or alkaline earth metal salt of an alcohol of formula Rxe2x80x94OH (II), where R is as defined above,
addition of water and oxidant,
extraction of the orthocarbonate, and
distillative work-up of the extract.
The reaction of trichloroacetonitrile with an alkali metal or alkaline earth metal salt of an alcohol of the formula II is conducted in a polar solvent. Examples of suitable solvents include ethers, such as, for example, tetrahydrofuran, dimethoxyethane, diisopropyl ether and dibutyl ether, polyethers, such as, for example, diethylene glycol dimethyl ether, sulfoxides and sulfolanes, such as, for example, dimethyl sulfoxide, sulfolane, 2-methylsulfolane, 3-methylsulfolane and 2-methyl-4-butylsulfolane, nitrites, such as, for example, acetonitrile, amides, such as, for example, dimethylformamide and N,N-dimethylacetamide, and the corresponding alcohols of the formula II. The solvent used is particularly preferably an alcohol of formula II.
The cations in the alkoxide compounds can be alkali metals or alkaline earth metals. Preference is given to sodium alkoxides and potassium alkoxides.
The temperature of the reaction are from xe2x88x9220xc2x0 C. to 200xc2x0 C., preferably from 50xc2x0 C. to 150xc2x0 C., very particularly preferably the reflux temperature of the reaction mixture.
The reaction of trichloroacetonitrile with alkoxide is conducted at a pressure ranging from 0.1 bar to 50 bar, preferably at a pressure ranging from 1 bar to 10 bar. The reaction is particularly preferably conducted at atmospheric pressure.
The alkoxides are prepared by known methods from the corresponding alcohols of formula II. These alkoxides are known compounds or can be prepared in a manner similar to the methods of preparing analogous, known compounds.
After the reaction, the reaction mixture is preferably stirred at the reflux temperature ranging from 10 minutes to 24 hours, preferably from 1 to 10 hours, very particularly preferably from 2 to 3 hours. The solvent used can, if desired, subsequently be completely removed by distillation. However, preferably, the solvent content is reduced in amount ranging from 10% to 90%, particularly preferably from 70% to 80%.
In order to dissolve the precipitated salt, a sufficient amount of water to which an oxidant has been added is added at a temperature ranging from 0xc2x0 C. to 90xc2x0 C., preferably at a temperature ranging from 5xc2x0 C. to 40xc2x0 C., on a small scale also particularly preferably at room temperature of about 20xc2x0 C. Besides chlorine or chlorine water, the oxidant used can also be, for example, polysulfide, thiosulfate, polythionate, hydrogen peroxide, hypochlorite or hypobromite solutions. A hydrogen peroxide solution is particularly preferred. The hydrogen peroxide solution added to the reaction mixture can have a concentration ranging from 0.1 to 70% by weight. A solution having a hydrogen peroxide solution concentration ranging from 3 to 50% by weight is preferred, particularly preferably about 3% strength by weight solution.
The extraction can be conducted continuously or batchwise at temperatures ranging from 0xc2x0 C. to 100xc2x0 C., preferably from 0xc2x0 C. to 50xc2x0 C., particularly preferably at room temperature of about 15 to 30xc2x0 C.
Suitable extractants include organic, aprotic solvents. Examples of suitable extractants include aliphatic hydrocarbons, such as, for example, pentane and hexane; cycloaliphatic hydrocarbons, such as, for example, cyclohexane, methylcyclohexane and ethylcyclohexane; aromatic hydrocarbons, such as, for example, toluene, ethylbenzene, xylenes, cumene and mesitylene; chlorinated hydrocarbons, such as, for example, dichloromethane, 1,1- and 1,2-dichloroethane and trichloromethane; ketones, such as, for example, methyl isobutyl ketone, methylcyclohexanone and diisobutyl ketone; and esters, such as, for example, ethyl acetate, butyl acetate and ethyl propionate. The extractant is preferably toluene or cyclohexane or particularly preferably methylcyclohexane. After phase separation and separation of the extractant from the crude product by distillation, the extractant can be used in other extraction operations.
Having now generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only and are not intended to be limiting unless otherwise specified.